Atipamezole which is 4-(2-ethyl-2,3-dihydro-1H-inden-2-yl)-1H-imidazole of formula I
is a well known pharmaceutical agent currently used as its hydrochloride salt in reversal of the effects of sedative-analgesic veterinary drugs.
The preparation of atipamezole hydrochloride salt is described in U.S. Pat. No. 4,689,339, wherein atipamezole obtained from the hydrogenation step is first recovered from alkaline solution as free base. After the evaporation of methylene chloride solvent to dryness the isolated crystalline product is converted into its hydrochloride salt by treatment with dry hydrogen chloride in ethyl acetate.